Biological interactions during ion exchange removal of ammonia from terrestrial and marine waste water
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Wastewater containing ammonia is a product of oil refineries, coal gasification plants, slaughterhouses, dairy plants, distilleries, fertilizer plants and pharmaceutical operations; ammonia is also found in municipal wastewater. The ammonia is toxic to living organisms and it is desirable that it be removed. The foremost aim of this research was to use biologically activated ion exchange materials for ammonia removal from wastewater. In the past sand, plastic media and activated carbon as well as some ion exchange materials, e.g., clinoptilolite, have been used like a solid surface for bacteria growth. In this work some other materials were used for a combined biological and ion exchange process. The materials used were mordenite and Macronet MN 500 for terrestrial water, and modified zeolites for selective uptake of ammonia from marine waters. Clinoptilolite was used for comparison, as an ion exchanger which previously has been biologically activated. The ammonia adsorption characteristics of the materials in saline and non-saline synthetic wastewater were determined and compared with literature data. The data was fitted using Langmuir and Freundlich isotherms. The effect of the individual presence of potassium, calcium and magnesium ion upon ammonium ion uptake onto each material was also investigated. Bench scale ion-exchange stirred cell experiments were conducted to assess the uptake kinetics of ammonium ion. Process parameters include: initial ammonia concentration, the agitation rate, material particle size and mass of the material. The suitability of the ion exchange materials as a support for the growth of nitrifying bacteria was determined by observing the nitrification process in the flasks containing different materials, for the fresh and saline media. The ion exchangers were tested in continuous columns initially without bacterial growth and later with. To overcome the problem of low oxygen levels in the column and to avoid over aeration of the system, a novel design of columns was introduced, where aeration through the column was achieved by the air permeable silicon tubing. The synthetic material MN 500 exhibited the highest uptake capacity but the natural zeolites had the highest preference for ammonium ions in the presence of interfering cations. The ion exchange materials removed ammonia from saline water. A product of zeolitic nature, ZZ, exhibited the highest uptake capacity for ammonia removal from saline water. Natural zeolites were shown to be better media for bacterial growth in non-saline water. MN 500 exhibited better ammonia removal performance for the combined process in sea water compared to modified zeolite, ZZ. Both the clinoptilolite and mordenite used in non-saline medium, exhibited higher uptake capacity during the column experiments than for batch experiments. By introducing bacteria into the column, the uptake capacity was increased from the value of 0.15 to the value of 0.22meq/g for clinoptilolite. The improvement for the biologically active mordenite was from the value of 0.30meq/g without bacteria to the value of 0.4 meq/g with bacteria. The aeration of 2.88dm³/h, achieved by the tubing, provided better condition for the nitrification within the column, compared to the commonly used tank pre-aeration at the rate of 180dm³/h. The biologically active ion exchange column was not efficient in removing ammonia from saline water. High salt concentrations and slower nitrification in saline medium interfered the process significantly. It could be concluded that biologically active ion exchange is acceptable method for ammonia removal from non-saline wastewater. The possible way to improve the efficiency of the process in saline water would be to apply it in wastewaters in with nitrifying bacteria are already established. Mordenite proved to be more adequate for biological activation compared to commonly used clinoptilolite, which indicates that more ion exchange materials should be tested for combined process. The new aeration system within the columns proved to be more efficient compared to the commonly used tank pre-aeration.